Radio base device reference signal, allocation method, and reference signal allocation program

ABSTRACT

A CS searches in advance for information about unique words used by neighboring CSs to hold the information in a storage unit. When an LCH establishment request is made by a PS in the cell of the CS, it is confirmed whether or not there is an empty traffic slot. Further, with reference to the unique word information of the neighboring CSs of the same frequency and the same slot as the empty slot to be allocated, an unused unique word pattern is allocated.

TECHNICAL FIELD

The present invention relates to a radio cell station apparatus, areference signal allocation method and a reference signal allocationprogram in a mobile communication system, and more particularly to aradio cell station apparatus, a reference signal allocation method and areference signal allocation program for allocating a reference signal toa terminal device that makes a connection request.

BACKGROUND ART

Recently, in a rapidly-developing mobile communication system, for animprovement of efficiency in use of radio wave frequencies, variousmultiple access systems have been proposed that allow a plurality ofusers to share a radio transmission path and conduct communicationssimultaneously, and are now partially in practical use.

For example, PHS (Personal Handyphone System) generally employs, as amethod of splitting a transmission channel, TDMA (Time Division MultipleAccess) that divides a radio channel with respect to time.

The TDMA system transmits respective digitized signals of users by radiowaves at different frequencies in separate and certain time periods(time slots), and separates respective signals of the users by frequencyfilters as well as time synchronization between a base station andrespective mobile terminal devices of the users.

Further, for a further improvement of efficiency in use of radio wavefrequencies, SDMA (Space Division Multiple Access) system in which asingle time slot of a single frequency is spatially divided to transmitdata of a plurality of users has been proposed.

In both of the TDMA system and the SDMA system, a time period (1 frame)using one frequency is divided into several time slots so as to alloweach user to use different time slot. Accordingly, time-position control(burst synchronization control) for accurately transmitting signals toallocated time slots in order to avoid overlapping of the signal withother user's transmission is required at the time of transmission.

In the PHS, synchronous position detection utilizing what is calledcorrelation synchronization has conventionally been known as a method oflocating a synchronous position of a signal received from a personalstation (hereinafter, referred to as “PS”) in a cell station(hereinafter, referred to as “CS”).

According to the synchronous position detection utilizing thecorrelation synchronization, a time-position at which a correlationvalue attains a peak is specified as the synchronous position in thefollowing manner. Specifically, in view of the fact that a receptionsignal from a PS includes in each frame a reference signal (a uniqueword signal: UW signal) section consisting of an already-known bitstring common to all users, a CS calculates correlation of analready-known waveform of the reference signal stored in a memory inadvance and a waveform section cut out while shifting the waveform of areception signal from the PS having a prescribed length.

The above-described correlation synchronization, however, is based onthe premise that the CS receives a signal from a single PS, and it isnot adapted to a case in which the CS receives signals of the samefrequency from two PSs in an overlapped manner.

In the SDMA in particular, a single time slot of the same frequency isspatially divided and resultant channels are allocated to a plurality ofPSs. Therefore, it is highly likely that two signals of the samefrequency arrive at the CS in an overlapped manner.

If synchronous positions of the reception signals from the PSs of theplurality of users coincide with one another, reference signal sectionsof the reception signals overlap with one another and the users cannotbe identified or separated from one another, resulting in interferenceamong the users.

In any systems other than the SDMA system as well, a CS in a certaincell could receive from a desired PS a signal of a certain frequency onwhich an unnecessary interference wave of the same frequency of anotherPS connected to a CS in a different cell overlaps.

The aforementioned event is likely to occur in a traffic-busy regionlike urban area in which CSs are densely placed. Since the synchronousposition of the signal received from the desired PS cannot be specified,interference also occurs between users in different cells, resulting indeterioration in communication quality.

In order to solve the problem above, control such as forming adirectivity pattern in accordance with a direction of the PS by means ofan adaptive array apparatus or slightly shifting a signal transmissiontime for each of the plurality of PSs establishing space divisionmultiple access has been carried out so far in the CS of the SDMAsystem.

In addition, recently, Japanese Patent Laying-Open No. 2001-231072, forexample, has proposed a measure to prevent mutual interference among aplurality of users by appropriately separating and extractingcommunication data of each mobile station by designating and usingdifferent reference signal for each PS in the CS.

Here, an operation for controlling allocation of a reference numberperformed by the conventional CS on each PS will be described withreference to FIG. 9.

FIG. 9 is a flowchart illustrating an operation performed by a controlunit within the CS when a link channel establishment request is receivedfrom the PS for initiating a call or data communication.

It is noted that, as the precondition for the operation in FIG. 9, areference signal is stored as unique word information in advance in aunique word storage unit within the CS in a fixed manner.

The unique word information represents information obtained byassociating a unique word value with information indicating a statusthat the unique word has been allocated. The unique word takes a 16-bitvalue such as “0011110101000110” expressed as a binary number, or a32-bit value. In addition, the unique word takes a value specifying a PSsuch as user 1, user 2 and so on as a value indicating a status that theunique word has been allocated, or a value indicating that the uniqueword has not yet been allocated.

Referring to FIG. 9, initially, when a link channel establishmentrequest is received from the PS (step S301) or when a link channelreestablishment request is received (step S302), a control unit searchesfor a channel available for allocation to the PS (step S303).

If there is no channel available for allocation (step S304), controlsuch that a link channel allocation rejection notification istransmitted to the PS is exerted (step S308).

On the other hand, if there is a channel available for allocation (stepS304), referring to the unique word held in the unique word storageunit, the control unit determines that an unallocated unique word is tobe allocated to the PS and updates the unique word information so as toassociate the unique word with the PS (step S305).

In addition, the control unit transmits to the PS a link channelallocation notification including notification of the determined, oneunique word (step S306).

Furthermore, the control unit provides a value of the unique wordincluded in the notification, to a reference signal generation unit in auser processing unit that carries out processing adapted to the PS (stepS307).

Thus, the conventional CS can determine the reference signal based onthe unique word value and appropriately direct, based on the referencesignal and a reception signal, a directivity pattern to the PS.Accordingly, interference with other PSs can be avoided andcommunication can be conducted with the PS in the SDMA system whilecommunication quality is retained.

The conventional CSs heretofore discussed are all techniques specific toSDMA to prevent mutual interference between a plurality of users in acell and thereby retain certain communication quality.

There still remains a problem, however, that the conventional CSs do notsufficiently address the problem of interference with users in anothercell.

For example, as shown in FIG. 9, even when the CS designates differentunique words for respective PSs in the cell, a unique word designatedfor one PS is not the one that is designated in consideration of any PSsin other cells. Therefore, in a certain time slot, the designated uniqueword could be identical to a unique word designated for a PS in anothercell. In this case, although interference with other PSs in the samecell can be avoided, interference with any PSs in other cells couldstill occur.

It is noted that the above-described situation is not peculiar to theSDMA system and could occur as well to the TDMA system.

An object of the present invention is therefore to provide a radio cellstation apparatus, a reference signal allocation method and a referencesignal allocation program that can avoid mutual interference between PSsin adjacent cells and thereby prevent deterioration in communicationquality.

DISCLOSURE OF THE INVENTION

According to an aspect of the present invention, a radio cell stationapparatus in a mobile communication system is provided and signalsreceived in the mobile communication system include already-knownreference signals. The radio cell station apparatus includes: searchmeans for searching for a reference signal already used in a neighboringcell station; storage means for storing the reference signal detected bythe search means; and reference signal allocation means for allocating,when a connection request is received from a terminal device, areference signal different from the reference signal stored in thestorage means.

Preferably, before the connection request is received from the terminaldevice, the search means receives in advance a communication signalcommunicated between a neighboring cell station and a terminal devicecommunicating with the neighboring cell station, and analyzes areference signal in use from the received communication signal, and thestorage means stores and holds the analyzed reference signal.

More preferably, the search means searches for the reference signal usedin the neighboring cell station for each traffic slot allocated to theterminal device.

According to another aspect of the present invention, a radio cellstation apparatus in a mobile communication system is provided andsignals transmitted/received in the mobile communication system includealready-known reference signals. The radio cell station apparatusincludes: storage means for storing a plurality of reference numbersdifferent from each other; and reference signal allocation means forrandomly selecting, when a connection request is received from aterminal device, a reference signal from the storage means based on acell station number assigned to each cell station and allocating thereference signal to the terminal device.

Preferably, the reference signal allocation means allocates an i-threference signal corresponding to value i of a reminder of division ofthe cell station number by total number m of reference signals stored inthe storage means, where m is a natural number and i is a natural numberof at most m.

According to still another aspect of the present invention, a referencesignal allocation method performed by a radio cell station apparatus ina mobile communication system is provided and signals received in themobile communication system include already-known reference signals. Thereference signal allocation method includes the steps of: searching fora reference signal already used in a neighboring cell station; storingthe reference signal detected; and allocating, when a connection requestis received from a terminal device, a reference signal different fromthe reference signal stored.

Preferably, the method further includes the steps of: before theconnection request is received from the terminal device, receiving inadvance a communication signal communicated between a neighboring cellstation and a terminal device communicating with the neighboring cellstation, and analyzing a reference signal in use from the receivedcommunication signal; and storing the analyzed reference signal.

More preferably, the method further includes the step of searching forthe reference signal used in the neighboring cell station for eachtraffic slot allocated to the terminal device.

According to a further aspect of the present invention, a referencesignal allocation method performed by a radio cell station apparatus ina mobile communication system is provided and signalstransmitted/received in the mobile communication system includealready-known reference signals. The method includes the steps of:storing a plurality of reference numbers different from each other; andrandomly selecting, when a connection request is received from aterminal device, a reference signal from the plurality of referencesignals based on a cell station number assigned to each cell station andallocating the reference signal to the terminal device.

More preferably, the method further includes the step of allocating ani-th reference signal corresponding to value i of a reminder of divisionof the cell station number by total number m of the reference signalsstored, where m is a natural number and i is a natural number of at mostm.

According to a further aspect of the present invention, a referencesignal allocation program performed by a radio cell station apparatus ina mobile communication system is provided, signals received in themobile communication system include already-known reference signals, andthe program is performed for a computer to execute the steps of:searching for a reference signal already used in a neighboring cellstation; storing the reference signal detected; and allocating, when aconnection request is received from a terminal device, a referencesignal different from the reference signal stored.

Preferably, the program is performed for the computer to further executethe steps of: before the connection request is received from theterminal device, receiving in advance a communication signalcommunicated between a neighboring cell station and a terminal devicecommunicating with the neighboring cell station, and analyzing areference signal in use from the received communication signal; andstoring the analyzed reference signal.

More preferably, the program is performed for the computer to furtherexecute the step of searching for the reference signal used in theneighboring cell station for each traffic slot allocated to the terminaldevice.

According to a further aspect of the present invention, a referencesignal allocation program performed by a radio cell station apparatus ina mobile communication system is provided, signals transmitted/receivedin the mobile communication system include already-known referencesignals, and the program is performed for a computer to execute thesteps of: storing a plurality of reference numbers different from eachother; and randomly selecting, when a connection request is receivedfrom a terminal device, a reference signal from the plurality ofreference signals based on a cell station number assigned to each cellstation and allocating the reference signal to the terminal device.

Preferably, the program is performed for the computer to further executethe step of allocating an i-th reference signal corresponding to value iof a reminder of division of the cell station number by total number mof the reference signals stored, where m is a natural number and i is anatural number of at most m.

Thus, in accordance with the present invention, deterioration in qualityof call and interference between users that are caused by mutualinterference between PSs in adjacent cells can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram showing a configuration of a radiocell station according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram illustrating information about uniquewords used by neighboring CSs that are held in storage unit 70 in FIG.1.

FIG. 3 shows a table of unique word numbers and their associated uniqueword patterns.

FIG. 4 schematically shows a form in which a plurality of PSs areconnected for each of CSs.

FIG. 5 is a flowchart illustrating an operation of the first embodimentthat is performed for allocation of unique words by a control unit ofthe radio cell station.

FIG. 6 generally shows a sequence of link channel establishment betweena CS and a PS according to the first embodiment.

FIG. 7 schematically shows a form in which a plurality of PSs areconnected for each of CSs.

FIG. 8 is a flowchart illustrating an operation of the second embodimentthat is performed for allocation of unique words by the control unit ofthe radio cell station.

FIG. 9 is a flowchart illustrating an operation performed by a controlunit of a conventional CS when a link channel establishment request isreceived from a PS.

BEST MODES FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described in detailhereinafter with reference to the drawings. The same or correspondingelements have the same reference characters allotted.

FIRST EMBODIMENT

FIG. 1 is a schematic block diagram showing a configuration of a radiocell station according to a first embodiment of the present invention.

Referring to FIG. 1, the radio cell station apparatus includes a radiounit 10, a plurality of antennas (four antennas of antennas #1 to #4,for example), a reception unit 20, a demodulation unit 30, a controlunit 40, a demodulation unit 30, a transmission unit 50, a modulationunit 60, and a storage unit 70.

Antennas #1 to #4 are connected to radio unit 10.

In reception, signals received by antennas #1 to #4 are provided toreception unit 20 through radio unit 10. The reception signals providedto reception unit 20 are subjected to various types of analog signalprocessing such as amplification and frequency conversion, and convertedto digital signals by an A/D converter (not shown). In addition,reception unit 20 separates and extracts a signal of each user under thecontrol of control unit 40. The separated and extracted reception signalof each user is provided to demodulation unit 30, and subjected tonecessary demodulation processing and time-division processing. Theoriginal signal is thus recovered and output to public switchedtelephone network (not shown) through control unit 40.

On the other hand, in transnission, a transmission signal provided fromthe public switched telephone network (not shown) is provided tomodulation unit 60 through control unit 40, subjected to necessarytime-division processing and modulation processing, and provided totransmission unit 50. In transmission unit 50, the transmission signalis converted to an analog signal by a D/A converter (not shown) andsubjected to various types of analog signal processing such asamplification and frequency conversion necessary for radio transmission.

In transmission, a signal from transmission unit 50 is supplied toantennas #1 to #4 through radio unit 10, and transmitted to a desired PSfrom antennas #1 to #4.

Specifically, control unit 40 is implemented by a CPU, and controls theentire CS. In particular, control unit 40 allocates a channel to the PSwhen control unit 40 receives a call from the PS through a controlchannel and when it receives an incoming call through the publicswitched telephone network (not shown).

Specifically, storage unit 70 is implemented by a memory that holds, ashereinlater described, information about unique words used byneighboring CSs as well as information about a unique word pattern tableand cell station numbers, and holds and reads the above-describedinformation according to instructions from control unit 40.

FIG. 2 is a schematic diagram illustrating information about uniquewords used by neighboring CSs that are stored and held in storage unit70 in FIG. 1.

Referring to FIG. 2, in storage unit 70, for each of a plurality of timeslots from which one frame is composed, data concerning unique wordsused by neighboring CSs in the same time slot is stored.

For example, for the time slot corresponding to slot number 1,information about unique words used by neighboring CSs is searched forand held for each of channels corresponding to frequencies available tothe CSs.

Here, the unique word information is searched for, before reception of alink channel establishment request from a PS, by control unit 40 of theCS. Control unit 40 receives traffic channel signals that aretransmitted by using empty slots to PSs in the cell from the neighboringCSs, and detects unique words included in the signals. Further, controlunit 40 receives traffic channel signals that are transmitted to the CSin the cell from PSs in the neighboring CSs, and detects unique wordsincluded in the signals. To the detected unique words, unique wordnumbers different from each other are assigned and the unique words areheld in storage unit 70.

Referring to FIG. 2, specifically, for a frequency in use, 30 ch, in thetime slot of slot number 1, unique words corresponding to unique wordnumbers 8 and 3 are detected from traffic channel signals fromneighboring CSs.

Further, it is seen that, for the frequency of channel 31 ch, uniqueword number 1 is used and, for the frequency of 32 ch, unique wordnumber 2 is used.

FIG. 3 shows a table of unique word numbers and their associated uniqueword patterns. The table of the unique word patterns is held, as theunique word information of neighboring CSs as discussed above, instorage unit 70 within the CS in advance.

Referring to FIG. 3, each unique word pattern that is stored for oneunique word number is constituted of a total of four patterns: a patternfor uplink consisting of 16 bits; a pattern for downlink consisting of16 bits; a pattern for uplink consisting of 32 bits; and a pattern fordownlink consisting of 32 bits.

This is because both of the uplink and the downlink of a channel betweenthe CS and the PS consist of a signal control channel (hereinafter,referred to as SCCH) for transmitting information necessary forconnecting a call and a traffic channel (hereinafter, referred to asTCH) used for communication, and because the SCCH and the TCH includeunique words consisting of 32 bits and 16 bits respectively.

For example, regarding unique word number 1, unique word pattern “8001h”is stored for the uplink of 16 bits. It is noted that this pattern is ahexadecimal notation of the 16-bit unique word pattern in binarynotation and the last character “h” means that this pattern is inhexadecimal notation.

Similarly, for the downlink of 16 bits, the uplink of 32 bits and thedownlink of 32 bits, “7fffh”, “11111111h” and “88888888h” are storedrespectively.

Regarding unique word number 2 and subsequent unique word numbers aswell, a set of four unique word patterns is stored for one unique wordnumber (not shown).

Therefore, referring again to FIG. 2 showing the unique word informationof the neighboring CSs, regarding the frequency in use of channel 31 chof slot number 1 for example, the unique word pattern of unique wordnumber 1 has already been used. Then, in light of the table in FIG. 3,it can be determined that the unique words of the aforementioned fourpatterns are used.

Next, a method of allocating unique words by the radio cell stationapparatus of the first embodiment having the above-describedconfiguration is described in connection with FIG. 4.

FIG. 4 schematically shows a form in which a plurality of PSs areconnected for each of CSs.

Referring to FIG. 4, radio waves from each of CSs (CS1 to CS5 forexample) are receivable within the boundary of the region indicated byeach of concentric circles (101 to 105 for example) having the CS at thecenter. In circles 101 to 105 each, a plurality of user PSs (not shown)are located and connected at a predetermined frequency of the CS inrespective time slots.

Here, in an urban area for example where cell stations are denselyplaced, as shown in FIG. 4, regions 101 to 105 where radio waves fromrespective CS1 to CS5 adjacent to each other are receivable overlap eachother. Therefore, a transmission signal from a PS in any portion whereadjacent regions overlap reaches both of respective CSs in the regions.

Here, for CS1 to CS4 each, a unique word is designated that is common toa plurality of user PSs in the cell. For example, to CS1, a unique wordassociated with unique word number 1 is provided.

It is supposed here that CS5 in FIG. 4 receives a link channel (LCH)allocation request from a user PS that requests connection. Then, it isdetermined whether or not there is an empty slot. If it is found thatthe cell station has an unused empty time slot, a link channel in theempty time slot is selected for the PS making the connection request.

Usually, to the empty time slot, other user PSs are not connected.Therefore, basically there arises no interference of radio waves, thelink channel is effectively selected and the allocation of the linkchannel to the PS is established.

If a unique word included in the allocated transmission channel is thesame as any unique word that has already been used by adjacent CS1 toCS4, however, interference with radio waves from user PSs and CSs inother cells could occur in the time slot to cause interference betweenusers in different cells.

Accordingly, when the PS is to be allocated to an empty transmissionchannel in a certain time slot, it is necessary to confirm that nointerference occurs with radio waves from any user PSs that have alreadybeen connected to adjacent CSs in the time slot.

In this case, therefore, CS5 refers to unique word patterns ofneighboring cell stations CS1 to CS4 stored in advance in storage unit70 in FIG. 1, selects and assigns a unique word pattern that is not usedin the time slot, thereby avoiding interference with any PSs in othercells.

Specifically, since adjacent four cell stations CS1 to CS4 have alreadyused unique word patterns associated with unique word numbers 1, 3, 4and 6, CS5 in FIG. 4 selects and allocates a unique word associated withan unused unique word number (5 for example).

Thus, interference with PSs in other cells connected to the same timeslot is avoided and deterioration in communication quality can beprevented.

FIG. 5 is a flowchart illustrating an operation of the first embodimentthat is performed for allocation of unique words by control unit 40 ofthe radio cell station apparatus in FIG. 1.

The configuration in the functional block diagram of the cell stationshown in FIG. 1 is executed in software in accordance with theflowcharts shown in FIGS. 5 and 8, actually by a not-shown digitalsignal processor (DSP). The DSP reads a program including each step inthe flowcharts shown in FIGS. 5 and 8 from a not-shown memory andexecutes the same. The program can be downloaded from a center (notshown) through a not-shown circuit control unit and a public network.

Referring to FIG. 5, control unit 40 in the CS of FIG. 1 initiallysearches for information about unique words used for each slot byneighboring CSs, and accumulates the information in storage unit 70(step S110).

Then, control unit 40 determines whether or not a link channel (LCH)establishment request is made by any user PS of the cell station (stepS102).

When the LCH establishment request is not received, control unit 40returns to step S101 to search for unique word information ofneighboring CSs until the LCH establishment request is made and updatesas required the information accumulated in storage unit 70.

When the LCH establishment request is received, control unit 40determines whether or not there is an empty traffic slot (step S103).

In step S103, when there is an empty traffic slot, it is then determinedwhether or not a traffic channel (TCH) can be allocated (step S104).

When no empty traffic slot is present, a link channel allocationrejection is transmitted (step S107).

In step S104, when it is determined that the traffic channel can beallocated, then, a unique word pattern to be allocated is determinedfrom the traffic slot to be allocated and the frequency to be used (stepS105).

At this time, control unit 40 refers to unique word patterns ofneighboring CSs accumulated in storage unit 70 to select an unusedunique word pattern.

Finally, information about notification of the LCH allocation includingthe value of the selected unique word is transmitted to the PS makingthe LCH allocation request (step S106), and the allocation is completed(step S108).

In step S104, when it is determined that the traffic channel (TCH)cannot be allocated, an LCH allocation rejection is transmitted to thePS (step S107).

FIG. 6 generally shows a sequence of link channel establishment betweena CS and a PS according to the first embodiment.

Referring to FIG. 6, receiving a link channel (LCH) establishmentrequest from the PS, the CS carries out the operation shown in FIG. 5 todetect an empty traffic channel and specify a unique word to beallocated to the PS based on the information about unique words used byneighboring CSs.

Further, the CS provides to the PS that makes the connection request, anotification of the link channel allocation including available slotnumber, frequency and unique word value.

Then, the PS receiving the notification of the allocation uses thedesignated information channel to transmit a synchronous burst signal tothe CS. Then, the CS returns the synchronous burst signal to the PS.Synchronization is thus established.

As discussed above, according to the first embodiment of the presentinvention, the CS allocates, to a PS making a connection request, a linkchannel including a unique word of a pattern different from any uniquewords having already been used by any neighboring CSs in a traffic slotto be allocated. Thus, interference with user PSs in other cells can beavoided to prevent deterioration in communication quality.

SECOND EMBODIMENT

FIG. 7 schematically shows a form in which a plurality of PSs areconnected for each of CSs.

A method of allocating a unique word by a radio cell station apparatusof a second embodiment is conceptually described in connection with FIG.7.

Referring to FIG. 7, like FIG. 4, the boundary in which radio waves fromeach of cell stations CS1 to CS5 are receivable is indicated by each ofconcentric circles 101 to 105 having the CS at the center. In FIG. 7,because of a high density of cell stations, concentric circles 101 to105 overlap each other.

It is noted that, in circles 101 to 105 each, a plurality of user PSsare located and connected at a predetermined frequency of the CS inrespective time slots.

Here, the radio cell station apparatus of the second embodiment differsfrom the radio cell station apparatus of the first embodiment in thatrespective CSs of the second embodiment have cell station numbers (BS)different from each other.

For example, CS1 has its cell station number of “100001” and CS2 has itscell station number of “100002”.

Thus, a unique word associated with the cell station number may bedetermined in advance to avoid coincidence between unique words ofdifference cell stations.

As an example, in FIG. 7, to cell stations CS1 to CS5, respective cellstation numbers and associated unique word numbers are providedrespectively. Here, the unique word number is uniquely determined as avalue corresponding to the reminder of division of the cell stationnumber by the total number (8 for example) of unique word patterns heldin storage unit 70 in FIG. 1.

Accordingly, since CS1 has its cell station number of “100001”, theunique word to be allocated is unique word number 1 corresponding to “1”which is the reminder of division of the cell station number by 8.

Similarly, CS2 having its cell station number of “100002,” is given aunique word corresponding to unique word number 2, and CS3 having itscell station number of “100003” is given a unique word corresponding tounique word number 3.

Namely, respective CSs have respective unique words different from eachother. Search for unique words used by neighboring CSs as conducted inthe first embodiment is thus unnecessary, and mutual interference withuser PSs in other cells can be prevented.

FIG. 8 is a flowchart illustrating an operation of the second embodimentthat is performed by control unit 40 of the radio cell station in FIG.1.

Referring to FIG. 8, initially control unit 40 determines whether or nota user PS of the cell station makes a link channel (LCH) establishmentrequest (step S201).

Then, when the LCH establishment request is received, control unit 40determines whether or not there is an empty traffic slot (step S202).

When the empty traffic slot is present in step S202, it is thendetermined whether or not a link cannel can be allocated for the trafficchannel (TCH) (step S203).

When the empty traffic channel is not present, a link channel allocationrejection is transmitted (step S207). It is noted that, when it isdetermined that the link channel cannot be allocated for the trafficchannel as well, the link channel allocation rejection is transmitted(step S207).

When it is determined in step S203 that the traffic channel can beallocated, a unique word pattern to be allocated is determined from acell station number (step S204). For example, as shown in FIG. 6, theunique word number to be allocated may be specified based on the valueof the reminder of division of the cell station number by the totalnumber of unique word patterns stored in storage unit 70.

Finally, the value of the unique word specified in step S204 is includedin information about notification of LCH allocation that is transmittedto the PS making the LCH allocation request (step S205), and theallocation is completed (step S206).

When it is determined that the TCH cannot be allocated, an LCHallocation rejection is transmitted to the PS (step S207).

As discussed above, according to the second embodiment of the presentinvention, the allocated unique word is different from any unique wordsused by any neighboring CSs and accordingly interference with users inother cells is reduced and communication quality can be ensured.

Further, since a unique word to be allocated is specified independentlyby CSs each based on the cell station number assigned to each cellstation, it is unnecessary to search for and store unique words used byneighboring CSs. Accordingly, the allocation of unique words issimplified and the circuit scale of the storage unit can be reduced.

It is noted that the techniques disclosed in the first and secondembodiments are not limited to the SDMA system and the TDMA system andare applicable to all access systems performing transmission andreception between a terminal and a cell station by the time-divisionmethod.

As heretofore discussed, according to an aspect of the presentinvention, the CS allocates, to a PS making a connection request, a linkchannel including a unique word that is different from any unique wordvalues having already been used by any neighboring CSs in a traffic slotto be allocated. Thus, interference with user PSs in other cells can beavoided to prevent deterioration in communication quality.

Further, according to another aspect of the present invention, anallocated unique word is different from any unique words used by anyneighboring CSs and accordingly interference with users in other cellsis reduced and communication quality can be ensured.

Furthermore, since a unique word to be allocated is specifiedindependently by CSs each based on the cell station number, it isunnecessary to search for and store unique words used by neighboringCSs. Accordingly, the allocation of unique words is simplified and thecircuit scale of the storage unit can be reduced.

INDUSTRIAL APPLICABILITY

It is thus seen from the above that the radio cell station apparatus,the reference signal allocation method and the reference signalallocation program of the present invention can avoid mutualinterference between PSs in adjacent cells, and accordingly are usefulfor a mobile communication system allowing a plurality of users to sharea radio transmission path.

1. A radio cell station apparatus in a mobile communication system,signals received in said mobile communication system includingalready-known reference signals, comprising: search means for searchingfor a reference signal already used in a neighboring cell station;storage means for storing the reference signal detected by said searchmeans; and reference signal allocation means for allocating, when aconnection request is received from a terminal device, a referencesignal different from the reference signal stored in said storage means.2. The radio cell station apparatus according to claim 1, wherein beforethe connection request is received from said terminal device, saidsearch means receives in advance a communication signal communicatedbetween said neighboring cell station and a terminal devicecommunicating with said neighboring cell station, and analyzes areference signal in use from the received communication signal, and saidstorage means stores and holds said analyzed reference signal.
 3. Theradio cell station apparatus according to claim 2, wherein said searchmeans searches for the reference signal used in said neighboring cellstation for each traffic slot allocated to said terminal device.
 4. Aradio cell station apparatus in a mobile communication system, signalstransmitted/received in said mobile communication system includingalready-known reference signals, comprising: storage means for storing aplurality of reference signals different from each other; and referencesignal allocation means for randomly selecting, when a connectionrequest is received from a terminal device, a reference signal from saidstorage means based on a cell station number assigned to each cellstation and allocating the reference signal to said terminal device. 5.The radio cell station apparatus according to claim 4, wherein saidreference signal allocation means allocates an i-th reference signalcorresponding to value i of a reminder of division of said cell stationnumber by total number m of reference signals stored in said storagemeans, where m is a natural number and i is a natural number of at mostm.
 6. A reference signal allocation method performed by a radio cellstation apparatus in a mobile communication system, signals received insaid mobile communication system including already-known referencesignals, comprising the steps of: searching for a reference signalalready used in a neighboring cell station; storing said referencesignal detected; and allocating, when a connection request is receivedfrom a terminal device, a reference signal different from said referencesignal stored.
 7. The reference signal allocation method according toclaim 6, further comprising the steps of: before the connection requestis received from said terminal device, receiving in advance acommunication signal communicated between said neighboring cell stationand a terminal device communicating with said neighboring cell station,and analyzing a reference signal in use from the received communicationsignal; and storing said analyzed reference signal.
 8. The referencesignal allocation method according to claim 7, further comprising thestep of searching for the reference signal used in said neighboring cellstation for each traffic slot allocated to said terminal device.
 9. Areference signal allocation method performed by a radio cell stationapparatus in a mobile communication system, signals transmitted/receivedin said mobile communication system including already-known referencesignals, comprising the steps of: storing a plurality of referencesignals different from each other; and randomly selecting, when aconnection request is received from a terminal device, a referencesignal from said plurality of reference signals based on a cell stationnumber assigned to each cell station and allocating the reference signalto said terminal device.
 10. The reference signal allocation methodaccording to claim 9, further comprising the step of allocating an i-threference signal corresponding to value i of a reminder of division ofsaid cell station number by total number m of said reference signalsstored, where m is a natural number and i is a natural number of at mostm.
 11. A reference signal allocation program performed by a radio cellstation apparatus in a mobile communication system, signals received insaid mobile communication system including already-known referencesignals, and said program performed for a computer to execute the stepsof: searching for a reference signal already used in a neighboring cellstation; storing said reference signal detected; and allocating, when aconnection request is received from a terminal device, a referencesignal different from said reference signal stored.
 12. The referencesignal allocation program according to claim 11, said program performedfor the computer to further execute the steps of: before the connectionrequest is received from said terminal device, receiving in advance acommunication signal communicated between said neighboring cell stationand a terminal device communicating with said neighboring cell station,and analyzing a reference signal in use from the received communicationsignal; and storing said analyzed reference signal.
 13. The referencesignal allocation program according to claim 12, said program performedfor the computer to further execute the step of searching for thereference signal used in said neighboring cell station for each trafficslot allocated to said terminal device.
 14. A reference signalallocation program performed by a radio cell station apparatus in amobile communication system, signals transmitted/received in said mobilecommunication system including already-known reference signals, and saidprogram performed for a computer to execute the steps of: storing aplurality of reference signals different from each other; and randomlyselecting, when a connection request is received from a terminal device,a reference signal from said plurality of reference signals based on acell station number assigned to each cell station and allocating thereference signal to said terminal device.
 15. The reference signalallocation program according to claim 14, said program performed for thecomputer to further execute the step of allocating an i-th referencesignal corresponding to value i of a reminder of division of said cellstation number by total number m of said reference signals stored, wherem is a natural number and i is a natural number of at most m.